Measurement device by pressurizing the subsoil and method for carrying out an associated pressurization test

ABSTRACT

The unit for measuring the volume of fluid comprises a device for measuring the mass of the fluid reservoir.

The present invention generally relates to a measuring device for pressurizing the subsurface, in particular a dilatometric measuring device or a pressiometric measuring device respectively intended to carry out a dilatometric or pressiometric test. For example, the pressiometric measuring device is a device of the Menard type, according to standard NFP 94-110-1.

More specifically, the invention relates to a measuring device for pressurizing the subsurface, comprising:

-   -   at least one pressiometric probe intended to be inserted into a         borehole in the subsurface, said pressiometric probe comprising         at least one deformable cell,     -   a fluid reservoir comprising a container and a volume of fluid         contained in the container,     -   a transfer unit configured to introduce the fluid from the fluid         reservoir inside the deformable cell, said unit comprising a         transfer member including a suction line fluidly connected to         said fluid reservoir, and a discharge line fluidly connected to         the deformable cell,     -   a unit for measuring the volume of fluid transferred from the         fluid reservoir to the inside of the deformable cell.

The pressiometric and dilatometric tests are load tests done in the subsurface, generally in a calibrated borehole, the analysis of which makes it possible to obtain mechanical properties of the subsurface, for example the pressiometric modulus E.

To perform this type of measurement, the deformable cell is pressurized, by increasing pressure plateaus, by injecting the fluid from the fluid reservoir using the transfer member of the transfer unit. For each pressure plateau, the injected volume of fluid is measured.

In the case of a pressiometric test, the pressiometric curve, or expansion curve, that is obtained by placing the pressure measured in the deformable cell on the x-axis and the variation in volume at the end of the corresponding pressure plateau on the y-axis, makes it possible to access the aforementioned mechanical properties.

In order to obtain reliable values of mechanical properties representative of the subsurface, it is necessary to obtain a precise measurement of the volume of fluid injected at the end of each applied pressure plateau.

It is possible to use a metering pump as transfer member, for example a piston pump or a membrane pump.

However, these types of pumps have drawbacks: piston pumps do not have a perfect seal, and the membrane of membrane pumps becomes distended and loses its initial shape as it is used.

Thus, this type of pump does not make possible to obtain the necessary measuring precision to carry out pressure tests in the subsurface, in particular for pressure plateaus greater than 80 bars.

To that end, the invention aims to propose a measuring device for pressurizing the subsurface of the aforementioned type, in which the unit for measuring the volume of fluid comprises a device for measuring the mass of the fluid reservoir.

Thus, by measuring the mass of the fluid reservoir before and after injecting fluid into the deformable cell, it is possible to obtain a precise determination of the volume of injected fluid irrespective of the nature of the transfer member used.

According to specific embodiments, the device includes one or more of the following features, considered alone or according to any technically possible combination(s):

-   -   the device further comprises an emptying line fluidly connected         to the discharge line and to the fluid reservoir, said emptying         line being configured to empty the fluid contained in the         deformable cell into the fluid reservoir;     -   the emptying line comprises a valve intended to control the         fluid flow rate in the emptying line;     -   the suction line and/or the emptying line are submerged in the         fluid reservoir;     -   the fluid reservoir comprises at least one side wall and one         lower wall, and the suction line and/or the emptying line have         no mechanical connection with said side wall and said lower         wall;     -   the device for measuring the mass of the fluid reservoir is         suitable for measuring a mass with a measuring error less than         or equal to 0.2 g;     -   the device for measuring the mass of the fluid reservoir is a         scale arranged below the fluid reservoir.

The invention also relates to a method for carrying out a test for pressurizing the subsurface with a measuring device defined above, comprising:

-   -   a step for inserting the pressuremeter probe into a borehole,     -   a step for introducing fluid from the fluid reservoir inside the         deformable cell using the transfer unit,     -   a first step for measuring a first mass of the fluid reservoir         before introducing fluid inside the deformable cell using the         device for measuring the mass of the fluid reservoir,     -   a second step for measuring a second mass of the fluid reservoir         after introducing fluid inside the deformable cell using the         device for measuring the mass of the fluid reservoir,     -   a step for determining the volume of fluid introduced inside the         deformable cell, comprising a sub-step for subtracting the         second mass and the first mass.

According to specific embodiments, the method comprises one or more of the following features:

-   -   the method further comprises a preliminary step for determining         the density of the fluid from the fluid reservoir and a step for         correcting the volume determined using said density;     -   the method further comprises:     -   a step for emptying fluid from the deformable cell toward the         fluid reservoir using the transfer unit,     -   a step for measuring a third mass of the fluid reservoir after         emptying the deformable cell into the fluid reservoir using the         device for measuring the mass of the fluid reservoir,     -   a step for comparing the first mass and the third mass of the         fluid reservoir,     -   a step for determining outside leaks of the measuring device.

Other features and advantages of the invention will emerge from the detailed description thereof that is provided below, for information and non-limitingly, in reference to the appended FIG. 1, which is a schematic view of the measuring device according to the invention.

FIG. 1 shows a schematic view of a measuring device for pressurizing 1 the subsurface 3.

The device 1 according to the invention is typically a dilatometric measuring device or a pressiometric measuring device intended respectively to perform a dilatometric test or a pressiometric test.

For example, the device 1 is a pressiometric measuring device of the Menard type, according to standard NFP 94-110-1.

The pressiometric and dilatometric tests are load tests done in the subsurface, generally in a calibrated borehole, the analysis of which makes it possible to obtain mechanical properties of the subsurface, for example the pressiometric modulus E_(M).

The measuring device 1 comprises at least one pressiometric probe 7 intended to be inserted into a borehole 5 in the subsurface 3. Said probe 7 comprises at least one deformable cell 9.

The device 1 shown in FIG. 1 includes a single pressiometric probe 7.

For example, the pressiometric probe 7 includes a single deformable cell 9 by fluid injection, also called “packet” by those skilled in the art. The deformable cell 9 of the device 1 is also known in the state of the art as a “measuring cell”.

Alternatively, the pressiometric probe 7 further includes two guard cells (not shown) containing gas and which frame the measuring cell.

The guard cells make it possible to guarantee that the deformation of the measuring cell is only radial and that the pressurization test is a planar deformation test.

For example, the pressiometric probe 7 of the device 1 according to the invention is a Menard probe according to standard NFP 91-110-1, advantageously a flexible sheath Francis COUR FC 60 pressiometric probe.

The Francis COUR FC 60 probe is for example described in patents FR 3,009,841 and FR 2,910,047 by the Applicant.

Alternatively, any pressiometric probe 7 may be used, and for example of type E or G according to standard NFP 91-110-1.

The device 1 according to the invention comprises a fluid reservoir 11. The fluid reservoir 11 comprises a container and a volume of fluid contained in the container.

The fluid reservoir 11 comprise a bottom wall 13 and a side wall 15.

The fluid reservoir 11 has any shape, for example cylindrical or parallelepiped.

The fluid is typically an incompressible fluid, for example water.

The device 1 also comprises a transfer unit 17 configured to introduce the fluid from the fluid reservoir 11 inside the deformable cell 9.

The unit configured 17 comprises a transfer member 19 including a suction line 21 fluidly connected to said fluid reservoir 11, and a discharge line 23 fluidly connected to the deformable cell 9.

The transfer member 17 is typically any pump suitable for injecting the fluid into said deformable cell 9 withstanding a pressure typically comprised between 10 bars and 150 bars, for example 80 bars.

Advantageously, the device 1 further comprises an emptying line 25 fluidly connected to the discharge line 23 and to the fluid reservoir 11.

The emptying line 25 is configured to empty the fluid contained in the deformable cell 9 into the fluid reservoir 11.

Typically, the suction line 21 and the emptying line 25 are submerged in the fluid reservoir 11.

Advantageously, the suction line 21 and the emptying line 25 have no mechanical connection to the side wall 15 and the bottom wall 13 of the fluid reservoir 11.

Thus, the suction line 21 and the emptying line 25 are positioned away from said bottom 13 and side 15 walls.

Typically, the emptying line 25 comprises a first valve 27 movable between an open position allowing the fluid to circulate to the fluid reservoir 11 and a closed position not allowing the fluid to circulate to the fluid reservoir 11.

Alternatively and/or additionally, the discharge line 23 comprises a second valve 29 movable between an open position allowing the fluid to circulate to the pressiometric probe 7 and a closed position not allowing the fluid to circulate to the pressiometric probe 7.

The measuring device 1 includes a pressure gauge 31 in order to measure the pressure precisely inside the deformable cell 9.

The measuring device 1 according to the invention further comprises a unit 33 for measuring the volume of fluid transferred from the fluid reservoir 11 to the inside of the deformable cell 9.

Advantageously, according to the invention, the unit 33 for measuring the volume of fluid comprises a device 35 for measuring the mass of the fluid reservoir 11. The measuring unit 33 measures both the mass of the container and the mass of the fluid in the container.

For example, the device 35 for measuring the mass of the fluid reservoir 11 is a scale arranged below the fluid reservoir 11.

The scale is typically an electronic scale known from the state of the art.

Evan tediously, the device 35 for measuring the mass of the fluid reservoir 11 is suitable for measuring a mass with a measuring error less than or equal to 0.2 g.

An embodiment by pressurizing the subsurface with a measuring device 1 according to the invention will now be described.

The method first includes a step for introducing the pressiometric probe 7 into a borehole 5 of the subsurface 3 so as to position the pressiometric probe 7 at a defined depth (measuring station).

The pressiometric or dilatometric tests are typically done at different depths along the borehole 5.

At each depth, the deformable cell 9 is pressurized by increasing pressure plateaus by introducing fluid from the fluid reservoir 11 inside the deformable cell 9 using the transfer unit 17.

The pressurization is for example done by successive increasing plateaus.

Typically, the number of pressure plateaus is comprised between 8 and 20, for example 12.

Alternatively, the deformable cell 9 is pressurized by successively injecting increasing volumes of fluid and measuring the pressure inside the corresponding deformable cell.

The pressure inside the deformable cell 9 is for example comprised between 1 bar and 500 bars based on the considered pressure plateau.

The corresponding volume of fluid injected inside the deformable cell 9 is typically comprised between 50 cm³ and 3000 cm³ based on the considered pressure plateau.

The method further comprises a prior step for measuring a first mass of the fluid reservoir 11 before introducing fluid inside the deformable cell 9 using the device 35 for measuring the mass of the fluid reservoir 11.

Then, the method comprises a step for measuring a second mass of the fluid reservoir 11 after introducing fluid inside the deformable cell 9 still using the device 35 for measuring the mass of the fluid reservoir 11.

By subtracting the second mass from the first mass and multiplying by a predetermined fluid density, the volume of fluid introduced inside the deformable cell 9 is then determined.

The steps described above are successively repeated for each pressure plateau and the variation in the volume of injected fluid is determined by subtracting the masses of the fluid reservoir 11 before and after each corresponding injection.

In the case of the pressiometric test, a pressiometric curve, or expansion curve, is then obtained by placing the pressure measured in the deformable cell 9 on the x-axis and the variation he in volume at the end of the corresponding pressure plateau on the y-axis.

These data are next analyzed in order to determine the mechanical properties of the subsurface.

When the last pressure plateau has been reached and the last measurement of injected fluid volume has been determined, the method typically comprises a step for emptying fluid from the deformable cell 9 toward the fluid reservoir 11 using the transfer unit 17 via the emptying line 25.

The method then advantageously includes a step for measuring a third mass of the fluid reservoir 11 after emptying the deformable cell into the fluid reservoir 11 using the device 35 for measuring the mass of the fluid reservoir.

The first mass and the third mass of the fluid reservoir 11 are then compared and the method comprises a step for determining any leaks outside the measuring device 1.

Typically, the pressiometric probe 7 is then moved vertically in the borehole 5 to be positioned at the following measuring station and the steps of the method are reiterated.

Advantageously, the method according to the invention comprises a preliminary step before any measurement during which the density of the fluid of the fluid reservoir 11 is determined. The measured density is then used to correct the volumes of fluid determined during the method.

Thus, the device according to the invention makes it possible to obtain reliable and precise values of the mechanical properties of the subsurface 3, in particular by precisely measuring the volume variations of fluid injected into the deformable cell 9.

The absence of contact between the emptying 25 and suction 21 lines and the bottom and side walls of the fluid reservoir 11 enables a precise determination of the successive masses of the fluid reservoir 11 and in fine the volume of fluid injected into the deformable cell 9.

The device 1 according to the invention also makes it possible to check, between each measuring station, that there are no leaks outside the device 1 by comparing the mass of the fluid reservoir 11 after the injection of fluid into the deformable cell 9 and the mass of the fluid reservoir 11 after emptying of the fluid from the deformable cell 9 into the fluid reservoir 11.

Lastly, the device 1 makes it possible to inject a significant volume of fluid into the deformable cell 9. Indeed, the injected volume is limited only by the size of the fluid reservoir 11 and the maximum capacity of the measuring device 35 of the mass of said reservoir. 

1. A measuring device for pressurizing the subsurface, comprising: at least one pressiometric probe intended to be inserted into a borehole in the subsurface, said pressiometric probe comprising at least one deformable cell, a fluid reservoir comprising a container and a volume of fluid contained in the container, a transfer unit configured to introduce the fluid from the fluid reservoir inside the deformable cell, said unit comprising a transfer member including a suction line fluidly connected to said fluid reservoir, and a discharge line fluidly connected to the deformable cell, a unit for measuring the volume of fluid transferred from the fluid reservoir to the inside of the deformable cell, wherein the unit for measuring the volume of fluid comprises a device for measuring the mass of the fluid reservoir.
 2. The measuring device for pressurizing the subsurface according to claim 1, further comprising an emptying line fluidly connected to the discharge line and to the fluid reservoir, said emptying line being configured to empty the fluid contained in the deformable cell into the fluid reservoir.
 3. The measuring device for pressurizing the subsurface according to claim 2, wherein the emptying line comprises a valve intended to control the fluid flow rate in the emptying line.
 4. The measuring device for pressurizing the subsurface according to claim 2, wherein the suction line and/or the emptying line are submerged in the fluid reservoir.
 5. The measuring device for pressurizing the subsurface according to claim 2, wherein the fluid reservoir comprises at least one side wall and one lower wall, and the suction line and/or the emptying line have no mechanical connection with said side wall and said lower wall.
 6. The measuring device for pressurizing the subsurface according to claim 1, wherein the device for measuring the mass of the fluid reservoir is suitable for measuring a mass with a measuring error less than or equal to 0.2 g.
 7. The measuring device for pressurizing the subsurface according claim 1, wherein the device for measuring the mass of the fluid reservoir is a scale arranged below the fluid reservoir.
 8. A method for carrying out a test for pressurizing the subsurface with a measuring device according to claim 1, comprising: a step for inserting the pressiometric probe into a borehole, a step for introducing fluid from the fluid reservoir inside the deformable cell using the transfer unit, a first step for measuring a first mass of the fluid reservoir before introducing fluid inside the deformable cell using the device for measuring the mass of the fluid reservoir, a second step for measuring a second mass of the fluid reservoir after introducing fluid inside the deformable cell using the device for measuring the mass of the fluid reservoir, a step for determining the volume of fluid introduced inside the deformable cell, comprising a sub-step for subtracting the second mass and the first mass.
 9. The method for carrying out a test for pressurizing the subsurface according to claim 8, further comprising a preliminary step for determining the density of the fluid from the fluid reservoir and a step for correcting the volume determined using said density.
 10. A method for carrying out a test for pressurizing the subsurface according to claim 8, further comprising: a step for emptying fluid from the deformable cell toward the fluid reservoir using the transfer unit, a step for measuring a third mass of the fluid reservoir after emptying the deformable cell into the fluid reservoir using the device for measuring the mass of the fluid reservoir, a step for comparing the first mass and the third mass of the fluid reservoir, a step for determining outside leaks of the measuring device. 